The invention relates to a method and an arrangement for processing a digitized picture with pixels.
Such an arrangement and such a method are disclosed in ITU-T Draft Recommendation H.263, Video Coding for Low Bitrate Communication, September, 1997.
In the arrangement disclosed in Video Coding, supra and in the method disclosed in Video Coding, supra, a digitized picture to be processed has pixels to which coding information is assigned in each case.
Coding information is to be understood hereinafter to mean brightness information (luminance value) and/or chrominance information (color value) assigned to the respective pixel.
The pixels are grouped into picture blocks, each picture block normally having 8*8 or 16*16 pixels.
The picture blocks are furthermore grouped into macroblocks, each macroblock having four picture blocks which contain coding information in the form of brightness information (luminance picture blocks), and two picture blocks which contain chrominance information (chrominance picture blocks).
In the picture coding method which is disclosed in Video Coding, supra and is configured in accordance with the H.263/V.2 standard, provision is made for using so-called difference-picture coding for coding a digitized picture.
It is precisely in the case where such difference-picture coding is used that, in the case of a moving camera which records a scene, or else in the case of a recorded scene which is subjected to changes, the problem arises that the recorded background is not stationary.
This problem area takes on particular significance in the use of such methods for picture coding in the context of a mobile communications device, for example in the case of use in the context of a video mobile phone.
A video mobile phone is to be understood to be an apparatus in which a camera for recording a sequence of pictures and a telephone are integrated in an apparatus, the telephone being a radio telephone.
In the case of customary difference-picture coding, in such a case of a greatly changing background, a high proportion of an available data rate for the communication is required for coding for the greatly changing background. This results in a smaller proportion of the available data rate remaining for an object of interest which can be seen in a foreground of the picture and which only changes slightly compared with the background. Accordingly, the quality of the respectively coded picture is too poor.
However, it is often desirable for an object situated in the foreground to have a good quality, while a poorer quality in the picture coding with low resolution is entirely acceptable for the background.
Video Coding, supra, describes that, in an optional coding mode (slice structured mode), the digitized picture is subdivided into rectangles, the so-called slices, and coding parameters are respectively allocated separately to each rectangle.
The coding parameters specify, inter alia, the quantization with which the object contained in the respective rectangle is to be coded.
This procedure disclosed in Video Coding, supra has the disadvantage that the entire picture has to be decomposed into individual rectangles. This leads to considerable inflexibility in the context of coding a digitized picture. A further disadvantage in the case of the procedure disclosed in Video Coding, supra is to be seen in the fact that only a uniform spatial resolution can be used for all the slices.
ISO/IEC JTC1/SC29/WG11, MPEG-4 Systems, Working Draft 4.0 of ISO/IEC 14496-1, A. Eleftheriadis, C. Herpel, L. Ward (ed.), Apr. 16, 1997 discloses an object-based picture coding method referred to as an MPEG-4 picture coding method. In this method, different objects within the digitized picture are coded separately from one another. The video data streams arising from the coding of the individual picture objects are combined using a multiplexer. The method in accordance with the MPEG-4 standard has the disadvantage, in particular, that, on account of the highly complex method of coding the individual video data streams, in the case of a multiplicity of picture objects to be coded, considerable computing power is required for coding in real time and for automatic generation. This results from the coded quantity of video data streams of a scene description describing the interaction of the individual picture objects within the digitized picture. The requisite computing power is currently not available particularly in the case of mobile communications devices, for example a video mobile phone.
K.-P. Karmann et al, Moving object segmentation based on adaptive reference images, Proceedings of EUSIPCO-90, pp. 951–954, Barcelona, September 1990 discloses a method for segmenting a picture into picture objects, the method being referred to as moving object segmentation.
DE 196 54 983 B discloses reducing block artifacts produced in the context of block-based picture coding by using a block edge filter.
WO 98 15915 A (Univ. Columbia) Apr. 16, 1998 discloses a method for processing a digitized picture with pixels, in which the pixels are grouped into picture blocks, in which the picture is segmented into at least a first picture object and a second picture object. At least one picture block being assigned to at least a part of an edge of the first picture object and in which information about the picture object is assigned to the at least one picture block.
WO 98 15915 A does not disclose that the method is used in a mobile communications device. However, this feature is disclosed in U.S. Pat. No. 5,771,102 (Pelz Rodolfo Mann et al) Jun. 23, 1998, where a method for transmitting pictures between mobile telephones is described.